Decreasing the roughage:concentrate ratio of a diet to determine the critical roughage part for beef cattle.

The critical roughage part (CRP) of 2 diet types was determined in a cross-over design with 6 double-muscled and 6 normally conformed Belgian Blue bulls fitted with rumen cannulae. The roughage:concentrate ratio was lowered weekly until signs of a lack of physical structure were observed. For diet 1, consisting of maize silage and concentrates, the initial proportion of maize silage was 25% of DM but it decreased weekly with 5% units of DM. For the second diet, consisting of wheat straw and concentrate, 12% straw (DM basis) was provided during the first week and thereafter the proportion of straw decreased weekly with 3% units of DM. Several directly observable parameters (rumen pH, feed intake, bloat, faecal consistency) were evaluated weekly for each bull. Apart from these direct indicators of acidosis, also other parameters, whose results were only available after the end of the trial, were determined (volatile fatty acid profile, lactic acid concentration, chewing time). The roughage part between the part fed when signs of a lack of physical structure was first observed and the part that was fed the week before, was considered as the CRP. Most animals showed no acute signs of clinical acidosis (directly observable parameters) and finished the trial on a 100% concentrate diet. However, in sacco rumen DM-degradabilities of maize silage, grass silage and wheat grain was depressed considerably when low roughage diets were fed. Based on all observed parameters, the mean CRP was calculated to be 14.7% for diet 1 and 8.1% for diet 2. The beef type (double-muscled or not) had no influence on the CRP.     

Effect of rumen-degradable protein balance deficit on voluntary intake, microbial protein synthesis, and nitrogen metabolism in growing double-muscled Belgian Blue bulls fed corn silage-based diet

Two trials were conducted to evaluate the effect of rumen-degradable protein balance (OEB) deficit on voluntary intake (trial 1), microbial protein synthesis, and N metabolism (trial 2) in growing double-muscled Belgian Blue bulls. In trial 1, six bulls (339 +/- 26 kg of initial BW) were used in a replicated 3 x 3 Latin square and received a diet of 60% corn silage and 40% concentrate with ad libitum intake (DM basis). Three concentrates were formulated by adding urea at the expense of barley to give similar dietary contents of intestinal digestible proteins, NE for fattening, and fermentable OM, but with different levels of OEB. Thus, 2 levels of OEB deficit (-23.7 and -9.2 g of OEB/kg of DM) were compared with a diet providing a slight OEB surplus (5.3 g of OEB/kg of DM). Voluntary DMI decreased linearly (P = 0.02) with decreasing rumen-degradable protein balance. This decrease in intake could explain the linear decrease in ADG observed when negative OEB diets were fed. In trial 2, six bulls (304 +/- 12 kg of initial BW) with cannulas in the rumen and proximal duodenum were used in a replicated 3 x 3 Latin square and fed diets similar to those used in trial 1 at an intake level of 85 g of DM/kg of BW(0.75). Diurnal variations of ruminal NH(3)-N and plasma urea-N concentrations were greatly influenced by the level of OEB in the diet. No differences in NDF and starch degradation in the rumen, microbial N flow at the duodenum, or efficiency of microbial protein synthesis in the rumen were noted among the levels of OEB in diets. The reductions of the OEB value from 5.3 g/kg of DM to -9.2 g/ kg of DM and -23.7 g/kg of DM were associated with reductions of 26.5 and 48.8% in urinary N output. Absolute amounts of N retained by the bulls increased significantly with the level of OEB in diets. Indeed, 51.4% of the incremental supply of N was excreted between -23.7 and -9.2 g of OEB/kg of DM diets, and 74.6% of the incremental supply of N was excreted between -9.2 and 5.3 g of OEB/kg of DM diets. Feeding diets characterized by an adequate intestinal digestible protein supply and a OEB close to -10 g of OEB/kg of DM could be a feeding strategy to reduce N losses from the farm with little effect on the animal performance and voluntary intake. Reduced OEB may reduce N excretion in the environment but may also result in decreased N retention.     

Growth- and breed-related changes of muscle bundle structure in cattle

The objective of this study was to investigate the changes in muscle fiber bundles of cattle of different breeds during growth. Different numbers of muscle fibers are surrounded by connective tissue to form bundles macroscopically visible as meat fibers or meat grain, a common meat quality trait. To determine the influence of breed and age on morphological characteristics of muscle fiber bundles, 4 cattle breeds with different growth impetus and muscularity were reared and slaughtered under experimental conditions. German Angus, a typical beef cattle; Galloway, a smaller beef type; Holstein Friesian, a dairy type; and double-muscled Belgian Blue, an extreme type for muscle growth, were used. Between 5 and 15 bulls of each breed were slaughtered at 2, 4, 6, 12, or 24 mo of age, and slices of semitendinosus muscle were removed. Muscle structure characteristics were determined by computerized image analysis. During growth, the muscle cross-sectional area enlarged (P < 0.001) about 5-fold in double-muscled Belgian Blue bulls and about 4-fold in the other breeds. This was a result of the enlargement (P < 0.001) of primary bundles and muscle fibers. The bundle size was similar (P > or = 0.15) in bulls of German Angus and Galloway in all age groups and was doubled (P < 0.001) in double-muscled Belgian Blue animals from 4 mo of age on. The Holstein Friesian bulls had the smallest (P < 0.001) muscle fiber bundles at 24 mo of age. The number of muscle fibers per bundle and the number of bundles per muscle remained nearly constant (P > 0.05) during growth. This supports the existing view that the structure of the muscle is already fixed in prenatal life. The double-muscled Belgian Blue bulls showed a more than 2.5-fold greater (P < 0.001) number of muscle fibers per primary bundle compared with the other breeds investigated. The larger muscle fiber bundles led to a smaller amount of connective tissue per muscle area in double-muscled cattle. The coarser grain of meat in double-muscled Belgian Blue bulls and in older animals was not related to greater shear force values.     

Animal performance, plasma hormones and metabolites in Holstein and Belgian Blue growing-fattening bulls

Six Holstein (light-muscled type) and six Belgian Blue bulls (double-muscled type) were fed a finishing diet. Average daily gain was 1.36 kg for the Holstein bulls vs 1.24 kg for the Belgian Blue bulls (P less than .05). Holstein bulls consumed more feed (2.3 vs 1.8 kg/100 kg body weight, P less than .001) than the Belgian Blue bulls. The dressing percentage (55.4 vs 65.8%, P less than .001) and the proportion of muscle (56.1 vs 71.3%, P less than .001) in the carcass were less, whereas the proportions of adipose tissue (28.3 vs 15.4%, P less than .001) and bone (15.7 vs 13.4%, P less than .05) were higher in the Holstein bulls. Plasma creatinine determined in samples obtained once a week was lower (11.0 vs 20.3 mg/liter, P less than .001) in the Holstein bulls. In contrast, Holstein bulls tended to produce more triiodothyronine (2.3 vs 1.8 nM, P less than .10), tetraiodothyronine (71.9 vs 54.7 nM, P less than .10) and insulin-like growth factor I (IGF-I; 340 vs 205 ng/ml, P less than .20) than the Belgian Blue bulls. Growth hormone, insulin, IGF-I and testosterone were measured at 20-min intervals during two 24-h periods. In wk 6, Holstein bulls tended to produce more growth hormone than the Belgian Blues, as indicated by higher total peak area (3,185 vs 2,431 ng), peak amplitude (34.1 vs 22.6 ng/ml, P less than .10) and baseline (4.6 vs 3.3 ng/ml, P less than .20). In wk 27, the trends were opposite.(ABSTRACT TRUNCATED AT 250 WORDS)     

The relationship between carcass characteristics,plasma hormones and metabolites in young fattening bulls

Six Belgian Blue bulls (double-muscled type) and six Friesian bulls were offered a fattening diet for 34 weeks. Plasma samples were obtained once a week and also every 20 min over a 24 h period, 7 weeks before slaughter.No differences were observed between the breeds in plasma glucose, urea and free amino nitrogen concentrations, while creatinine was significantly higher in the Belgian Blue bulls. Tri-iodothyronin, tetra-iodothyronin, insulin-like growth factor 1, insulin and testosterone concentrations were higher in the Holstein group. In contrast, the Belgian Blue bulls appeared to produce more growth hormone. The slaughter weight, carcass weight, dressing percentage and proportion of lean meat were significantly higher in the Belgian Blue group. The characteristics of muscle mass (carcass weight, dressing percentage and proportion of lean meat) were positively correlated with creatinine and with the total peak area or peak amplitude of growth hormone. The insulin concentration was positively correlated with the proportion of adipose tissue in the carcass and negatively correlated with the proportion of muscle. There were no correlations between the carcass characteristics and insulin-like growth factor 1 or testosterone. No further information was provided when the ratios of the hormones were correlated with carcass characteristics.     

Feed intake of young double-muscled bulls fed on grass and supplemented with sugar-beet pulp.

Daily dry matter intake in young growing double-muscled bulls, fed indoors on grass, was estimated based on forty-four intake data from 28 animals, ageing at least five months and weighing up to 400 kg live weight. Intake was measured during five consecutive days using one of eighteen cuts of grass. Fresh meadow grass (mainly Lolium perenne) was fed ad libitum and two kg dried sugar-beet pulp was offered per animal and per day. Animal live weight averaged 278 +/- 82 kg and mean total daily dry matter intake amounted to 5.05 +/- 1.59 kg or 73.6 +/- 13.7 g per kg metabolic weight, while pulp dry matter intake amounted to 1.49 +/- 0.50 kg per day. Regression analysis showed that animal as well as feed characteristics could explain up to approximately 90% of the variation in daily dry matter intake. The supplementation resulted in an extra daily dry matter intake of 0.68 g per g pulp dry matter. Intake of double-muscled animals was considerably lower than previously reported for non-double-muscled cattle. An extra supplementation of young grazing double-muscled animals could be advised from these findings, while extra protein should also be considered.     

Energy requirement for maintenance and growth of Nellore bulls and steers fed high-forage diets

Data from three comparative slaughter experiments with individually fed Nellore bulls (n = 31) and steers (n = 66) were utilized to determine their NEm and NEg requirements when fed high-forage diets. The experimental design provided ranges in ME intake, BW, and ADG for the development of regression equations to predict NEm and NEg requirements. The Nellore bulls (Trial 1) were divided into two intake levels (ad libitum and 65% of the ad libitum). The steers (Trials 2 and 3) were allocated to three intake levels (ad libitum and 55 and 70% of the ad libitum). In both trials, there were three slaughter groups within each intake level. The three end points for the bulls were different days on treatment (100, 150, and 190 d and 130, 180, and 200 d, respectively, for older and younger animal subgroups). The steers were slaughtered when animals of the ad libitum treatment reached 400, 440, and 480 kg shrunk BW (SBW) on average for the first, second, and third group, respectively. For all body composition determinations, whole empty body components were weighed, ground, and subsampled for chemical analysis. In each of the trials, initial body composition was determined with equations developed from a baseline slaughter group, using SBW and empty BW (EBW), fat (EBF), and protein (EBP) as variables. The NEm was similar for bulls and steers; NEm averaged 77.2 kcal/ kg0.75 EBW. However, the efficiency of conversion of ME to net energy for maintenance was greater for steers than for bulls (68.8 and 65.6%, respectively), indicating that bulls had a greater ME requirement for maintenance than steers (5.4%; P < 0.05). Our analyses do not support the NRC (2000) conclusion that Nellore, a Bos indicus breed, has a lower net energy requirement for maintenance than Bos taurus breeds. An equation developed with the pooled data to predict retained energy (RE) was similar to the NRC (2000) equation. A second equation was developed to predict RE adjusted for degree of maturity (u): RE = (6.45 - 2.58/u) x EWG x e(0.469) x u), where u = current EBW/final EBW in which final EBW was 365 kg for steers and younger bulls and 456 kg for older bulls at 22% EBF, respectively.     

Effects of restricted and ad libitum intake of diets containing wheat middlings on site and extent of digestion in steers

A 5 x 5 Latin square design was used to determine the effects of restricted and ad libitum intake of diets containing wheat middlings on the site and extent of digestion compared to ad libitum intake of a corn-based diet and ad libitum intake of chopped alfalfa hay. Five ruminally and duodenally cannulated Angus steers (519 +/- 41.5 kg BW) were used to compare five dietary treatments. The five treatments were as follows: ad libitum access to a corn-based finishing diet (control), the control diet with 25 percentage units of the corn and soybean meal replaced with wheat middlings offered ad libitum (WM), the WM diet restricted to 75% of predicted ad libitum intake (RWM), the RWM diet with wheat middlings replaced with ammoniated wheat middlings (RNWM), and ad libitum access to a chopped alfalfa hay diet. Although RWM steers were fed to consume 75% of ad libitum intake, RWM steers consumed 15.5% less DM than WM. Steers fed ad libitum hay consumed 28.6, 31.7, and 37.2% less (P < 0.01) DM, OM, and nitrogen than RWM steers. No differences in apparent or true ruminal digestibility were observed among steers fed the control vs WM, WM vs RWM, RWM vs RNWM, or RWM vs hay diets. However, the steers fed the hay diet had 32.5, 33.4, and 36.9% lower (P < 0.01) apparent total tract digestibilities of DM, OM, and N than those fed the RWM diet. Average ruminal pH was lower (P < 0.01) for control steers than those fed the WM diet and for those fed RWM compared to the hay diet. The acetate:propionate ratio was higher for cattle fed hay vs the RWM diet. Microbial DM and OM flow to the small intestine was higher (P < 0.02) for steers fed the RWM diet than those fed the hay diet. In addition, bacterial N flow to the small intestine was higher (P < 0.01) for cattle receiving the RWM diet than the hay diet. Feeding diets containing 25 percentage units of wheat middlings at 75% ad libitum intake had no effect on ruminal digestibility.     

Growth performance, diet apparent digestibility, and plasma metabolite concentrations of barrows fed corn-soybean meal diets or low-protein, amino acid-supplemented diets at different feeding level

Two experiments, each with 36 barrows with high-lean-gain potential, were conducted to evaluate apparent nutrient digestibilities and performance and plasma metabolites of pigs fed corn-soybean meal diets (CONTROL) and low-protein diets. The low-protein diets were supplemented with crystalline lysine, threonine, tryptophan, and methionine either on an ideal protein basis (IDEAL) or in a pattern similar to that of the control diet (AACON). Amino acids were added on a true ileally digestible basis. The initial and final BW were, respectively, 31.5 and 82.3 kg in Exp. 1 and 32.7 and 57.1 kg in Exp. 2. In Exp. 1, the CONTROL and IDEAL diets were offered on an ad libitum basis or by feeding 90 or 80% of ad libitum intake. Pigs were fed for 55 d. In Exp. 2, the CONTROL, IDEAL, and AACON diets were offered on an ad libitum basis or by feeding 80% of the ad libitum intake. Pigs were fed for 27 d. Pigs fed the CONTROL diet had greater (P < 0.05) ADG and feed efficiency (G/F) than pigs fed the IDEAL (Exp. 1 and 2) and AACON diets (Exp. 2). As the level of feed intake decreased, ADG decreased (P < 0.05), but G/F tended to improve (P < 0.10) for pigs fed 90% of ad libitum in Exp. 1 and for pigs fed 80% of ad libitum in Exp. 2. In Exp. 1, the apparent total tract digestibilities of DM and energy were greater (P < 0.01) for pigs fed the IDEAL diet than for pigs fed the CONTROL diet. In Exp. 2, the apparent total tract digestibility of protein was greatest in pigs fed the CONTROL diet (P < 0.05) and was greater (P < 0.05) in pigs fed the AACON diet than in pigs fed the IDEAL diet. Plasma urea concentrations were lower in pigs fed the IDEAL diet than in pigs fed the CONTROL diet, regardless of feeding level. For pigs fed the CONTROL diet, plasma urea concentrations were lower when feed intake was 80% of ad libitum (diet level, P < 0.01). In summary, pigs fed the IDEAL and the AACON diets gained less and had lower plasma urea concentrations than pigs fed the CONTROL diet. Based on these data, it seems that the growth potential of pigs fed the IDEAL and AACON diets may have been limited by a deficiency of lysine, threonine, and(or) tryptophan and that the amino acid pattern(s) used was not ideal for these pigs.     

Response to virginiamycin in finishing beef bulls fed a maize silage diet or a complete dry feed

Two experiments have been conducted to study the effect of virginiamycin in a maize silage diet (I) or a complete dry feed (II). Virginiamycin was incorporated at 0 or 65 mg per kg concentrate which was fed at 0.75% of the live weight of 43 Belgian white-red bulls (I), or at 0 or 25 mg per kg complete dry feed for 24 Belgian white-blue bulls (II). In the first experiment daily gain was increased by virginiamycin from 1.28 to 1.38 kg without effect on intake, but with an improved feed conversion from 5.99 to 5.60 kg dry matter/kg gain. In the second experiment daily gain, daily dry matter intake and feed conversion were not influenced by virginiamycin. The differences between experiments may suggest that the response to virginiamycin probably depends on the diet type, although no significant interaction was found between diet type and virginiamycin with regard to growth rate (P greater than 0.10). In both experiments, fasting weight loss, dressing percent and carcass classification and composition were not affected by virginiamycin.     

Plasma hormones and metabolites in cattle in relation to breed (Belgian Blue vs Holstein) and conformation (double-muscled vs dual-purpose type)

Four Belgian Blue double-muscled type (BBDM) bulls, four Belgian Blue dual-purpose type (BBDP) bulls and four Holstein bulls were used in a fattening trial in order to relate differences in the extent of muscle development and adiposity to differences in digestibility, endocrine status, protein and lipid metabolism. The larger muscle development in BBDM animals was associated with a trend to higher nitrogen retention, higher food conversion efficiency (p<0.05) and lower apparent digestibility (p<0.05). No difference was found between the groups for plasma glucose concentration. Higher creatinine, lower -amino nitrogen, lower triglycerides and higher non-esterified fatty acid plasma levels were observed in BBDM as compared to Holstein bulls (p<0.05), the BBDP group being intermediate. A trend to a higher cholesterol plasma level was found in BBDM animals. There was no difference between the three groups in plasma fatty acid composition, except for the C_14:0 content. Some of the differences in plasma metabolites were related to carcass composition and endocrine regulation, a decrease in muscle development and an increase in adiposity being associated with lower growth hormone production (p<0.05) and higher insulin (p<0.05) and IGF₁ secretions. The insulin/growth hormone ratio at the end of the fattening period was 0.0011, 0.0018 and 0.0069 in BBDM, BBDP and Holstein bulls, respectively, and was directly associated with fat deposition.Abbreviations BBDM Belgian Blue breed double-muscled type - BBDP Belgian Blue breed dual-purpose type - IGF₁ insulin-like growth factor 1 - NEFA non-esterified fatty acids - T₃ triiodothyronin - T₄ tetraiodothyronin     

Effects of feeding growing cattle high-concentrate diets at a restricted intake on feedlot performance

Three trials were conducted to compare effects of restricted intake of high-concentrate diets vs ad libitum intake of corn silage diets during the growing phase on feedlot cattle performance. In Trial 1, 120 steers (initial BW, 246 kg) were fed 1) a corn silage-based diet ad libitum, 2) a high-moisture corn-corn silage-based diet with intake restricted to a level 20% less than that of the corn silage diet or 3) a high-moisture corn-based diet with intake restricted to a level 30% less than that of the corn silage diet. Steers fed the 20% restricted corn-corn silage-based diet tended (P = .07) to gain slower than those fed the corn silage or 30% restricted high-concentrate diet. Feed efficiency and diet digestibility were greatest for steers fed the 30% restricted-intake, high-concentrate diet (P less than .01). Performance of steers during the subsequent 118-d finishing period was not affected (P greater than .65) by source of energy during the growing period. In Trial 2, ADG of steers fed the 30% intake-restricted, high-concentrate diet was lower (P less than .01) than that of steers with ad libitum access to corn silage. During the 84-d growing period, steers fed supplemental blood meal had 8.3% greater gains and a 6% greater efficiency of feed use than those fed supplemental soybean meal (P less than .01). Monensin did not affect (P = .82) performance of steers fed 30% restricted-intake diets. During the 76-d finishing period, gains and feed conversion were improved (P less than .01) for steers fed the restricted-intake diet in the growing period compared with those given ad libitum access to corn silage. During the growing period in Trial 3, ADG of steers restricted-fed an all-concentrate diet were slightly greater (P less than .10) than ADG of those given ad libitum access to corn silage. Gains did not differ (P = .37) during the subsequent finishing period when steers were switched to 85 or 100% concentrate diets. We concluded that intake of all concentrate diets can be restricted to achieve gains equal to those of steers given ad libitum access to corn silage-based diets without detrimental effects on finishing performance.     

Excess crude protein for nongravid gilts

Twenty-five nongravid crossbred gilts (avg initial wt, 126 kg) were placed on either a high (38%) or a low (13%) crude protein (CP) diet and fed either at the rate of 1.82 kg/d or had ad libitum access to feed. In addition, a fifth group was pair-fed the 13% CP diet to the average intake of the gilts fed high CP ad libitum. The experimental period lasted 30 d. Corn-soybean meal diets were used and CP levels were varied by altering the corn:soybean meal ratio. Gain and gain/feed were reduced (P less than .01) in gilts fed 1.82 kg/d compared with the gilts fed ad libitum or pair-fed gilts. Gain (P less than .03) and feed intake (P less than .01) of gilts with ad libitum access to the 13% CP diet were higher than those of gilts with ad libitum access to the 38% CP diet. Gain/feed was not different (P greater than .10) between the two groups, however. Rate of gain and feed efficiency of gilts pair-fed the 13% CP diet were similar (P greater than .10) to those of gilts with ad libitum access to the 38% CP diet. Plasma total free amino acids, NH3 and total protein were not (P greater than .10) affected by treatment. Plasma urea-N and urinary total N, urea-N and orotic acid were increased (P less than .01) in gilts fed the high CP diet regardless of feed intake level. However, urinary NH3 was higher (P less than .01) in gilts fed the low-protein diet. These results indicate that excess dietary CP for nongravid gilts decreases gain and feed intake and has no effect on efficiency of feed utilization, but it increases plasma urea-N and urinary total N, urea-N and orotic acid.     

Determination of the methionine requirement of growing double-muscled Belgian blue bulls with a three-step method

The three-step technique was used to determine the requirements of total amino acids (TAA) and the first-limiting amino acid (AA) in growing double-muscled Belgian Blue bulls (BBb). In Exp. 1, three double-muscled BBb weighing initially 306 +/- 28 kg received a basal diet consisting of 30% meadow hay and 70% concentrate that was poor in digestible protein but had adequate NE because of continuous infusion of dextrose into the duodenum. The intestinal apparent digestibility of essential AA (EAA) was defined according to their duodenal and ileal flows. It averaged 72% but varied between 60% for Met and 79% for Arg. In Exp. 2, five double-muscled BBb (334 +/- 22 kg) received the same diet supplemented with duodenal infusions of dextrose and four doses of Na-caseinate (28, 56, 84, and 112% of intestinal digestible dietary AA) in a 4 x 4 Latin square design with one additional animal. Nitrogen retention for the basal diet alone and the four increasing supplements of Na-caseinate reached 49, 61, 70, 80, and 86 g/d, respectively. Nitrogen utilization improved from 34.3% without Na-caseinate supplementation to a maximum of 40.6%, with the third dose supplying 788 g/d of apparently digestible AA. Based on patterns of plasma concentrations, Met, Phe, and Arg were probably the limiting AA when animals optimized N utilization. In Exp. 3, six double-muscled BBb (315 +/- 25 kg) fed the basal diet received duodenal infusions of dextrose and AA, equivalent to the third dose in Exp. 2, except for digestible Met (9.3, 14.4, 18.4, 22.4, 26.4, and 30.4 g/d) in a 6 x 6 Latin square design. The Met requirement was close to 26.4 g/d on the basis of N retention.     

Protective effect of clenbuterol on duodenal epithelium during food restriction in rats

The aim of the study was to examine the effect of the beta2-adrenoceptor, clenbuterol, on the duodenal epithelium of food-restricted rats. Clenbuterol was administered as a dietary admixture (4 mg/kg diet) to three groups of male Wistar rats (n = 8) housed individually in metabolic cages and fed ad libitum for 15 days at 110% and 160% of the estimated requirement for energy maintenance. Untreated groups at each energy intake level were also included. Samples of the duodenum were examined by light microscopy. Compared with control animals, clenbuterol treatment significantly increased body mass in all diet groups, although it induced no changes in mean food intake. Gastrointestinal (GIT) dry mass was increased by clenbuterol only in the most severely-restricted-diet group. In this group, clenbuterol treatment increased GIT tissue nitrogen (23%), more than it did in the ad libitum group (13%). In all treated groups, clenbuterol induced significant hypertrophy of duodenal enterocytes and circular muscle layers, and the diameter of lymphatic vessels increased. In the clenbuterol-treated, restricted-diet groups the height of the brush borders of enterocytes increased. It is concluded that clenbuterol has a protective effect on the intestinal structure in rats on restricted as well as ad libitum diets.     

Body composition and tissue accretion rates of barrows fed corn-soybean meal diets or low-protein, amino acid-supplemented diets at different feeding levels

Two experiments, each with 39 high-lean-gain potential barrows, were conducted to evaluate the organ weights, body chemical composition, and tissue accretion rates of pigs fed corn-soybean meal diets (CONTROL) and low-protein diets supplemented with crystalline lysine, threonine, tryptophan, and methionine either on an ideal protein basis (IDEAL) or in a pattern similar to that of the control diet (AACON). Amino acids were added on a true ileally digestible basis. The initial and final BW were, respectively, 31.5 and 82.3 kg in Exp. 1 and 32.7 and 57.1 kg in Exp. 2, and pigs were fed for 55 and 27 d in Exp. 1 and 2, respectively. In Exp. 1, the CONTROL and IDEAL diets were offered on an ad libitum basis, or by feeding 90 or 80% of ad libitum intake. In Exp. 2, the CONTROL, IDEAL, and AACON diets were offered on an ad libitum basis, or by feeding 80% of the ad libitum intake. Three pigs were killed at the start of the experiments and three from each treatment were killed at the end of each experiment to determine body chemical composition. In both trials, the whole-body protein concentration (g/kg) and the accretion rates of protein (g/d) were greater (P < 0.05) for pigs fed the CONTROL than for pigs fed the IDEAL and AACON diets. In Exp. 1, pigs fed the CONTROL diet had a trend (P < 0.10) for greater water and lower lipid concentration and had greater (P < 0.05) water and ash accretion rates. Whole-body protein concentration was greatest (P < 0.05) in pigs fed at 80% of ad libitum, but protein, water, and ash accretion rates were greatest (P < 0.05) in pigs allowed ad libitum access to feed. In summary, pigs fed the IDEAL and the AACON diets had less protein in the body and lower protein accretion rates than pigs fed the CONTROL diet. It seems that reductions in protein deposition in pigs fed the IDEAL and AACON diets may have been due to a deficiency of one or more essential amino acids or possibly to increases in the NE for metabolic processes leading to increases in adipose tissue deposition.     

Effect of graduated vitamin D3 doses and different ration composition on the 25OH-vitamin D3 plasma concentration and fattening and slaughter production of bulls]

In a individual feeding experiment (348 days) 24 fattening bulls were given either a ration high in roughage (2.8 kg concentrate mixture, wheat straw ad libitum: group I) or high in concentrate (5.6 kg concentrate mixture, wheat straw ad libitum group II) supplemented with various levels of vitamin D3 (0, 250, 500, 1,000, 2,000, 4,000 and 8,000 IU per 100 kg body weight (bw) and day) and minerals as required. After 58, 101, 134, 172, 205, 277 and 340 days 25-OH-D3 plasma concentration was estimated. Fattening and slaughtering parameters were measured. The 25OH-D3 plasma concentration was significantly influenced by vitamin D3 supply, kind of ration and day of taking samples. 25-OH-D3 plasma concentration decreased below 5 ng per ml when vitamin D3 supply was less than or equal to 250 IU per 100 kg bw and day. The initial plasma levels were maintained when 500 IU vitamin D3 per 100 kg bw and day was given (6.6 ng per ml). Administration of greater than or equal to 1,000 IU per 100 kg bw and day increased 25OH-D3 plasma level (greater than 10 ng/ml). Plasma 25OH-D3 concentration was significant higher when bulls consumed diets rich in concentrate (10.6 and 18.2 ng/ml for I and II after 340th day). Differences in content of cell walls and crude fat of rations may be responsible for results. Daily weight gain of bulls amounted to 712 and 945 g when fed diets I or II. Dry matter intake and live weight gain were not significantly influenced by different vitamin D3 supply. Clinical symptoms of rachitis did not appear.     

Influence of level of dietary protein or energy on effects of ractopamine in finishing swine.

The effect of ractopamine, a beta-adrenergic agonist, on growth, nutrient utilization, and carcass composition was studied in pigs fed either 18% CP, 12% CP, or 18% CP restricted (RES = 67% of ad libitum) diets. The 18 and 12% CP diets provided 3.52 and 3.68 Mcal of DE/kg, respectively. All pigs were fed a low-protein (12% CP) diet during pretreatment growth from 15 to 60 kg. Ractopamine at 20 or 30 ppm (30 ppm for RES pigs) in the diet was fed from 60 kg live BW until slaughter at 105 kg (9 pigs/treatment). No ractopamine treatment effect (P greater than .05) was observed for either daily gain or gain/feed, although gain/feed was improved by 8% in both of the ad libitum groups. Ractopamine treatment resulted (P less than .01) in an overall reduction of carcass lipid by 8%, an increase of carcass protein by 5%, and a 21% improvement in the efficiency of protein utilization; the greatest changes occurred in the pigs fed the 12% CP diet (-17%, +11%, and +32%, respectively). The ad libitum daily feed intake was 15% less for pigs fed the 12% CP diet than for those fed the 18% CP diet (P less than .01), and there was a 10% reduction in intake of both diets with the addition of ractopamine (P less than .05). Both carcass lipid and protein deposition seemed to be closely related to energy intake (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of altering nutrient density (concentrate to roughage ratio) and restricting energy intake on rate, efficiency and composition of growing lambs

Two hundred ninety-eight Rambouillet ewe and wether lambs approximately 9 mo old from Texas were allotted to pens (29 to 30 lambs/pen). Two replicate pens were fed each of five diets. Two methods of restricting energy intake were evaluated: altering nutrient density (55% vs 72.5% vs 90% concentrate levels) and restricting intake of the 90% concentrate pelleted diet (92.5% or 85% ad libitum intake). Daily gains were highest with the 72.5% concentrate level and feed efficiency was poorest with the 55% concentrate diet fed ad libitum. Altering nutrient density did not reduce energy intake because lambs compensated by increasing feed intake at the lower nutrient densities. Actual feed intake was 89.5% of ad libitum for the 92.5% of ad libitum intake level and 84% of ad libitum at the 85% of ad libitum intake level due to refusal to consume some fines from the 90% concentrate diet. Feed refusal was greatest for lambs with ad libitum access to feed. Average daily gain was depressed by 8% at the 85% intake level. However, feed efficiency was improved (P less than .01) by 20% when intake was restricted to 92.5% of the ad libitum intake level. Differences in carcass traits were small, but consistent; carcass fat content was reduced slightly by restricting feed intake at constant slaughter weight.